The present invention relates generally to position, distance measuring, and navigation systems, and more particularly to improvements in a system for determining position, distance measuring, navigation, and feature and related information on golf courses to enhance the enjoyment of the game, speed of play, and efficiency of course management.
In golf players are more comfortable and more likely to excel on courses with which they are familiar. It is customary for a golfer on a new or little-played course to seek to gain at least some familiarity with the layout of each hole before starting play. Armed with this information, the golfer can approach each tee box during play of the course, knowing, for example, whether the particular hole is a `dog leg left`, a `dog leg right`, or straight; the general locations of hazards, such as sand traps, bunkers, and water traps on the hole; and locations of range postings, if any, for calculating yardage from the golfer's location to the front and rear of the green, the pin (cup), a hazard, and a desired lay up position for the green approach shot.
Golf courses have traditionally made available course layout and feature information booklets in the pro shop, for just such purposes. Yardage markers typically are placed at sprinkler heads along each hole, to provide range information from that point to the center of the green. These serve as aids to the player, but they also contribute to slowing the pace of play of the course. Slow play has an adverse effect on the course's daily revenue, as well as on other golfers' enjoyment of the game.
Proposals made to improve golf course information systems include use of buried electrical wires in various layouts on the course for interaction with mobile overland components (e.g., U.S. Pat. No. (USPN) 5,044,634 ("the '634 patent"); and use of radio direction finding or triangulation techniques (e.g., U.S. Pat. No. 4,703,444 ("the '444 patent") and U.S. Pat. No. 5,056,106).
More than twenty years ago, the U.S. government established a Global Positioning System (GPS) that uses space satellites and ground based stations to determine distance, range, and position, primarily for defense purposes, but which has found many uses for such information in various industrial and commercial applications. Earth-orbiting satellites provide reference points from which to determine the position of a point on or near the earth, using ground-based receivers. The satellite orbits are monitored by the ground station GPS receivers, and the travel times of signals received from the satellites are used to measure distance to each satellite. Each signal from a satellite is coded to permit the receiver to determine the elapsed time between transmission of the signal from the respective satellite and reception at the GPS receiver antenna, and thereby to calculate the distance as the product of elapsed time and speed of light. Receivers are not restricted to large ground stations, but may be portable, mobile and hand-held units for a multitude of private navigation, position and distance-measuring systems.
Distance measurements to three GPS satellites are used to accurately define the position of an object such as a GPS receiver, which may be stationary or moving, on or near the earth's surface. A fourth satellite enables verification of clock timing in the GPS system. With several satellites in "view", and using a computer, distances between objects can theoretically be measured almost instantaneously with great accuracy. But as a practical matter even small errors that typically occur in the calculated measurement of satellite signal travel time from system and natural phenomena can substantially reduce the accuracy of the distance and position calculations. Error causing phenomena include atmospheric propagation, receiver contributions, satellite ephemeris, and satellite clock. Errors have been purposely introduced in the satellite signals by the government to deny civilian users full accuracy. The combined effect of these errors can be as high as 100 meters or so.
In co-pending patent application Ser. Nos., 08/423,295 and 08/525,905, filed Apr. 18, 1995 and Sep. 8, 1995, respectively, assigned to the same assignee as the present application ("the '295 and '905 applications"), improvements are disclosed in golf course positioning and yardage measuring systems utilizing differential GPS (DGPS) (see, for example, Blackwell, "Overview of Differential GPS Methods", Global Positioning System, vol. 3, pp. 89-100, The Institute of Navigation, Washington, D.C. (1986)). With DGPS, errors in distance measuring applications are reduced by broadcasting error correction information from a ground receiver of known location in the vicinity of the user. The difference between a known fixed position of a GPS receiver and its position calculated from the satellite GPS signal fixes the error in the signal, and a continuous correction is provided for all other receivers, fixed or mobile, in the reception area. Knowing the error allows all distance and position calculations at the user's receiver to be corrected.
The golf course positioning and yardage measuring systems of the '295 and '905 applications use unique filtering algorithms, among other things, to offer much greater accuracy and reliability than would be found with conventional DGPS systems. An efficient, yet inexpensive communications network is used for data transmission between a base station and golf carts, with a variable length communication network that allows golf carts to be readily added or removed from the network. The systems of those co-pending applications employ high resolution color graphics displays on board the golf carts and at the course administrator's base station. Other advantages include detecting when the golf cart is within predetermined zones or regions of the course for use in unique features such as automatic display of the current hole on the cart monitor, measuring the pace of play for each hole, and providing automatic pop-up golf tips and advertisements on the cart monitor as the cart transitions from one hole to the next. The monitor is mounted in the roof of the cart in a way that gives the user excellent color readability in sunlight.
The PROLINK.TM. yardage and course management system disclosed in the '295 and '905 applications (PROLINK is a registered trademark of Leading Edge Technologies, Inc. of Chandler, Ariz., the assignee of the invention disclosed herein and in the '295 and '905 applications) includes a golf cart-based subsystem (or, alternatively, a hand-held or other roving unit) that uses state-of-the-art DGPS technology, together with various enhancements in--hardware and software. The system creates, stores, and displays a color graphical representation or map of the golf course on a video monitor in the cart or a liquid crystal display ("LCD") of a hand-held unit. Each hole of the course is selectively displayed with all of its hazards and features, with an icon representing the fixed or changing position of the roving unit superimposed in real time on the map of the hole being played. The golfer is provided by the system with an accurate measurement of the distance from the current position of the cart (e.g., at the tee box or other location on the hole) to the current pin placement, a hazard, or any other feature of the hole.
The PROLINK.TM. system provides many advantages to the golfer without burdening or significantly changing the way the course or any particular hole is played, or how business is conducted by course management--advantages such as real-time, accurate indications of distance (typically within two meters) from the cart to significant course features--green, pin, hazards on fairway, etc.; a relatively large, high resolution, color display with the capability for selection of a map of the entire course or any individual hole or other detailed feature; and a capability of individualize communications and messaging to and from the cart. The hole display and yardage functions in the cart system are activated automatically as the cart approaches the tee box at commencement of play of each hole. A movable cursor on the display allows the player to point to any feature on the displayed map to obtain a precise yardage measurement from the position of the cart. An automatic zoom feature increases the selected target area resolution, such as to view the contour of the green or the details of a particular hazard. The PROLINK.TM. system also enables the player to make consistently better and faster club selection from the information concerning target distance and hole layout.
The course management portion of the PROLINK.TM. system includes a base station computer unit, receiver/transmitter unit and video monitor in the clubhouse (or other desired location) to give the course administrator better insight into daily operations and revenues by providing a capability to identify, locate and monitor movement of every golf cart on the course in real-time; to use that knowledge to pinpoint and analyze the cause of bottle-necks on the course; to compile an extensive computerized data base useful for statistical insight into course operations and techniques for instituting improvements; and to communicate with all carts on the course, and to enhance course revenues through advertising and promotions broadcast to the cart monitors.
The PROLINK.TM. system also employs a technique and method for collecting survey data to map the layout of the golf course including such features as tee boxes, greens, fairways, cart paths, water hazards and sand traps. The collected survey data is post-processed and efficiently stored in memory in vector form for later retrieval and display. This data representing the golf course layout is used to efficiently determine the location of a golf cart relative to predetermined zones or regions. The system uses a zone detection algorithm and creates a number of different zones corresponding to areas such as features or portions of holes on the course. Accordingly, the PROLINK.TM. system can detect a golf cart within an established zone on the hole being played or elsewhere on the course from the cart coordinates. The zone detection algorithm enables various features of the system to be implemented, such as automatic hole display on the cart monitor as the cart enters the tee box zone of a new hole, and automatic pop-up advertisements or promotions or golf tips when the cart is in transition from one hole to the next.
Despite the capabilities of GPS and DGPS systems for their intended purpose, in golf course and other positioning, distance measuring, and ranging applications, such systems suffer loss of signal and, therefore, loss of communication and capability, when the roving unit moves behind an obstruction. On the golf course, this is particularly troublesome where the course is heavily treed, or quite hilly, or has on-course or adjacent buildings or other structures, or all of these types of obstructions, of sufficient dimensions to obscure or interfere with strong signal transmission. In these conditions, the golfer is inevitably faced with an "out-of-service" display screen on the cart monitor.
Co-pending U.S. patent application Ser. No. 08/690,962 titled "Robust Golf Navigation System" filed Aug. 1, 1996 in the names of J. Coffee et al. and commonly assigned with this application (hereinafter "the '962 application") discloses a dead reckoning system that overcomes these problems. The ACUTRAK.TM. golf course yardage and information system (ACUTRAK is a trademark of Leading Edge Technologies, Inc.), as that system is called, employs the advantages of a dead reckoning-based yardage system, with support of DGPS for calibration purposes only, and combined with the full-featured management and information capabilities of the PROLINK.TM. system. In the ACUTRAK.TM. system, the desirable attributes of a dead reckoning system are combined with limited aspects of a GPS system, through optimal estimation computer algorithms preferably using a Kalman filter, to achieve a significant synergistic improvement in performance of a golf course position, distance measurement, navigation, information, and course management system over a wide operating envelope.
The ACUTRAK.TM. system is golf cart-based, but could be packaged alternatively in smaller vehicles, even a set of golf bag wheels equipped with a mobile unit or a hand-held unit used with a pedometer version of the wheel-tracking system disclosed in the 0.007 application. That system utilizes virtually all of the features of the PROLINK.TM. system disclosed in the co-pending '295 and '905 applications, except for the ACUTRAK.TM. system's limited reliance on DGPS, as a calibration technique only. In addition, the ACUTRAK.TM. system has a unique guidance system in the form of a dead reckoning system that tracks the distance moved by and the orientation of the wheels, extrapolated to the heading or bearing of the golf cart (or other roving unit) in which a portion of the overall system is incorporated. The ACUTRAK.TM. system is unaffected by even frequent inability to view a satellite navigation system, such as the GPS satellites, requiring only relatively infrequent calibration during play to avoid a gradual increase or buildup of error in measurements as the cart is driven about the course. Thus, instead of experiencing frequent out-of-service indications on the cart monitor, the golfer is cognizant only of continuous, reliable operation of the ACUTRAK.TM. system.
A significant percentage of golf courses in the United States and elsewhere, notably Japan, employ a "cart path only" rule which requires that the golf cart (whose use is mandatory for play of the course) be restricted to cart paths, and that it not be driven on the fairway. Even for many courses where the "cart path only" rule is not in effect at all times, it is a requirement in limited instances where the course "manicure" may be affected by allowing carts to be driven on the fairway, such as where inclement weather is being experienced, or the course is wet from recent rain or even following sprinkler usage, such that the carts could produce ruts and adversely affect play of the course by biasing the roll of the ball. Moreover, even those courses which do not normally impose a cart path only rule because the paved cart paths themselves are limited to either end of the hole, i.e., at the tee box area and the green area, still preclude driving the cart directly onto the grass or terrain in either of those areas, that is, off the paved path. Where the cart path only rule is not uniformly imposed, it may be invoked from time to time on a daily basis by the course administrator who is generally the club's professional golfer and instructor, dubbed the "club pro", working from the clubhouse at which the course monitoring equipment for the PROLINK.TM. or ACUTRAK.TM. systems would be located.
It is a principal object of the present invention to take advantage of restrictions imposed on cart usage on a golf course to a cart path only rule, even in those limited situations where the rule applies only at the start and end of play of each hole, or even only in the vicinity of prescribed locations on each hole such as the green, to provide the cart navigation system, whether solely dead reckoning or combined with another navigational capability such as GPS, with a novel technique for intermittent calibration to eliminate or reduce position and measurement error buildup in the cart navigation system during play of the course.